Apparatus for determining the percentage of carbon in alpha specimen of iron or steel



v 1,526,005 Apnl .J. G. MALMBERG ETAL APPARATUS FOR DETERMINING THEPERCENTAGE OF CARBON IN A SPECIMEN OF IRON OR STEEL Original Filed Feb.5. 2 3 Sheets-Sheet 1 'NVENTORS: CARL JOHAN sum/Wm MAI-MBLM; \TOHANcu/v/vm? HoL sTRm BY: 814 M AT TORNEY 1,626,0U5 c. J. G. MALMBERG ET ALAPPARATUS FOR DETERMINING THE PERCENTAGE OF CARBON IN A SPECIMEN OF IRONon STEEL April 26 1927.

3 Sheets-Sheet 2 Original Filed Feb. 5. 2

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f Ml WE w R M 6 w T n T m 9 J /h p Y i w 1,626,005 G- MALMBERG ET ALNING THE PERCENTAGE OF CARBON IN A April 26,1927. J.

APPARATUS FOR DETERMI SPECIMEN OF IRON OR STEEL Original Filed Feb. 5.1921 3 Sheets Sheet 3 I N V E N T 0 R S. (an JOHAN GUN/VAR MALM ERG JobA cum/w HOLM ATTORNEY Figure l in an enlarged scale.

Patented Apr. 26, 1927.

CARL JOI'IAN GUNNAR MALMBERG, OF SURAHAMMAR, AND JOHAN GUNNABHOLMSTRI6M{OF SALTSJO-S'I'ORANGEN, SWEDEN. I

APPARATUS FOR DETERMINING THE PERCENTAGE, OF CARBON IN A SPECIMEN or 7IRON OR STEEL.

Original application filed February 5, 1921, Serial No. 442,895, and inSweden December 22, 1917.

' Divided and this application filed June 26, 1924. Serial No. 722,623.

The present invention has for its object an apparatus for determiningthe peipentage of carbon in a specimen of iron or steel and theapparatus is constructed with regard to a measuring method whichconsists in subjecting the specimen to repeated magnetization anddemagnetization between two chosen values of the magnetizing force andmeasuring the diiierence between the magnetic fluxes through thespecimen at said two values, this application being a. division of ourapplication Serial No. 442,895, filed February 5, 1921.

It has been found that when an iron specimen is subjected to theinfluence of a magnetic field. which is varied several times (to andfro) =between two values. the definitedifference of the magnetic fluxindicates the percentage of carbon of the specimen. The specimen must bemagnetized and demagnetized repeatedly between the .two chosen valuesbefore the difference in magnetic flux is measured, as it hasbeen foundthat said difference is constant only after several magnetizations anddemagnetizations.

Figure 1 in the annexed drawing explains the mere theoretical fact.

Fig. 2 represents diagrammatically the complete apparatus; 7

Fig. 3 is a vertical sectional view of a detail thereof; and

Figs. 4 and 5 illustrate modifications of certain elements of theapparatus. The magnetization of the specimen is as sumed to be variedbetween the values H and H of the magnetizing force. To these valuescorrespond then the flux densities I and I stated on the ordinates.According. to the present invention neither the values I nor the value Iforms the basis for the determination of the percentage of carbon, butthe difference between these two values.

The object of the repeated magnetization and demagnetization is alsoexplained in The highest possible flux density corresponding to themagnetizing force H is not obtained on the demagnetization following thefirst magnetization. The highest possible flux density is obtained onlyafter the specimen has been magnetized and demagnetized several times.The zigzag-line of the diagram is .suflicient period at a approachgradually an ultimate position. When this position has been reached itcan be said that the flux density of the specimen consists of twoportions: a fixed value I and a fluctuates magnetizing between the twomagnetizin force values H and 1-1,, As before state experiments haveconfirmed that it is this loose value or the magnetic loss indemagnetizing from the value H tothe value H which can be used as adirect indication of the percentage of carbon.

It has also been found that it is advantageous with regard to accuracyand rapidity in making the test that the specimen has pronouncedresidual pro erties. In order to obtain such properties the specimenshould be hardened by heating it for a sufliciently high temperature andthen rapidly cooling it.

In practice the magnetic loss between two values of the magnetizingforceshould be measured by means of a suitable instrument. The constant .ofthe apparatus is determined empirically by measuring the percentage ofcarbon'of a standard specimen. Thepercentage of carbon can then be readeither from acurveor a table or on the scale of the instrument,empirically graduated.

The measurement of the magnetic loss can of course be made in variousways, for instance by means of a. magnetometer or by the ballisticmethod. The latter method is preferred for practical reasons as theinfluence of external magnetic fields then can be avoided, for instanceby the use of a moving coil instrument with a tightly closed magneticcircuit.

According to the present invention it is possible to measure thepercentage of carloose value 1 -1 which latter with the magnetizing andthe denetic flux of certain iron specimens. How- For facilitating theadjustment of the ever, it is not possible to use any one of theseinstruments directly for determining the percentage of carbon accordingto the above. described method. Many incidental circumstances disturband make it impossible to obtain exactly the same results-for instancefor the same specimen in the same apparatus but on different occasions.Only after eliminating or reducing such circumstances to a minimum theabove measuring method becomes suitable for technical pur.- poses. Theconstructiow'ot a reliable magnetic measuringinstrument is the object ofthe invention. 7

As pointed out above, it is necessary that the measurement of I,-I, canbe done rapidly and reliably. The ballistic method.

must in this connection be considered the best one. The instrumentsusually used in connection with the method, in which the specimen isinserted in a primary induction coilin which the current flows andanouter secondary coil connected to the ballistic galvanometer, cannotbe used partly because the magnetic leakage cannot then be kept constantfor the same specimen, neither with closed nor with open magneticcircuits, and partly because the heat produced by the primary currentcauses changes of temperature which alters the resistance of the secondary coil, and also that of the iron. 'In the present invention thesedisturbing factors have been eliminated partly by arranging magneticscreens at the two ends of the iron specimen and the secondary coil andpartly by making the magnetizing and demagnetizing in an externalmagnetic circuit-relative to the screens, by means of a permanentmagnet. The permanent magnet can be moved in relation to the remainingpart of the magnetic circuit or one or more soft iron pieces can bemoved between the permanent magnet and the magnetic circuit of thespecimen (the screens), whereby said iron pieces when moved alternatelyeither open and close or close and short circuit the magnetic circuit.By using permanent magnets, the heating disturbances of the primarycurrent may be wholly eliminated. However, in order to obtain constancyalso the variations in the magnetizing forces must be compensated. 1

In the present invention this problem is solved by using a narrow airgap, which may be adjusted and is inserted in the magnetic circuit. Asthe permanent magnets lose their magnetism (the changes usually occur inthis direction) the air gap maybe more closed, thus rendering themagnetizing and the demagnetizing constant. This air gap (or air gaps)is adjusted by inserting a standard in the apparatus and altering theair gap until the indiction determined for the standard has beenobtained.

magnetic circuit very accurately also amagnetic shunt may be used inaddition to the said air-gap. As the constancy of the instrument is, assaid before, of very great importance, the circuit of the magnet as wellas that of the specimen must be pro-v tected against disturbing magneticfields which is done by enclosing the apparatus in an iron box. Themagnetic leakage is thus rendered constant in each separate case andchanges of the intensity of the magnetic field due to outside influencesprevented.

In the above description of the method it is pointed out that the curvesof magnetization and demagnetization gradually approach their ultimateposition. This position is theoretically reached only after an infinitenumber of magnetizations, but in practice only a few such magnetizationsare required. It is, however, necessary to keep the error. which ariseswhen the magnetizations and demagnetizations are stopped too soon, sosmall that it does not impair the accuracy of the method It is thereforealways necessary to make preliminary magnetizations in sufficient numberbefore the loss is measured. The apparatus must therefore be soconstructed that this measurement cannot be made unless a certain statednumber of magnetizations and demagnctizations have been made. Thetechnical carbometer must therefore include a device which automaticallymakes these preliminary magnetizations. This is preferably carried outby means of a clockwork Carbometcrs constructed according to the abovedescribed invention are shown in Figure 2.

The apparatus shown in these illustrations consists of a coil 2 woundwith many turns of insulated copper wire 3, a ballistic galvanometer 4,of suitable sensibility and damping, and a device for magnetizing anddemagnetizing the specimen 1 (Figure 3) between the two magnetizingvalues chosen for the apparatus.

)Vhen the magnetization and the deniagnetization is made, as describedhereafter, the coil 2 with the winding 3, in which the specimen isplaced. must be furnished with magnetic screens 5 and 6 of soft iron(see Figures 2 and 3) in order to obtain constant leakage.

The specimen should be cast in a mould and when hardened and placed inthe coil, it. forms an essential part of a; magnetic circuit theremaining magnetic resistance of which is constant. For the purpose ofprcventing the head of a specimen. which head may have various shapesand sizes, from exerting any influence upon the magnetic flux in thecircuit, the screens 5 and 6 are inserted. These screens are arranged atsuch a distance from each other (or the specimen is of such a length)that the cylindrical part of the specimen magnetlcally connects theplates 0 and 6. while the head 7 .is completely outside the one plate.

The ballistic galvanometer 4 is of usual moving coil' type and suitablyfurnished with a lens movable over the scale for accurate reading of then'iomentary indication, corresponding to the magnetic loss of the chosendifference in magnetizing forces.

As seen in Figure 2 the magnetic screens 5 and 6 of the coil areintended and pass through holes in the shield 83 of non-mag neticmaterial attached to the protecting box (frame) of the apparatus.

The coil 2 is supported by the bracket 92, also attached to the shield83. Close to the ends of the screens 5 and 6 are two long pieces of softiron 7 5) and 80 movably mounted which in the position hown in thefigure conduct the magnetic field emanating from the steel magnet 53 tothe screens 5 and 6. The magnetic circuit then-flows through the upperpole 53, the parts 795 the specimen,-the parts 680 the lower pole 53. Asthe iron pieces 7 9 and 80 are movable so that they can be moved awayfrom the position in which they conduct the magnetic field from and tothe magnet 53, the field flowing through the specimen is practicallydiminished to a alue near'zero, when the iron pieces are moved away. Theperiodical magnetization and demagnetization is c0nsequently made bymeans of the iron pieces 79 and 80 which are moved to and from the poition, shown in Figure 2. This is effected in the construction nowdescribed by fixing the pieces to a rotary shaft 78, but it is evidentthat the motion may be a recipro- 'ating or other motion. In the Figure2 the pieces 79 and 80 are assumed to be fastened in a drum ast ofnon-magnetic material. One end of the shaft 78 is mounted in the shield83, and the shaft extends through a hole in the shield 84, also ofnon-magnetic material and attached to the protecting box, and the otherend is fitted in the cross piece 85 which isnon-magnetic and fixedto theframe. The shaft 78 is actuated by the pinion 82 mounted on the shaft,said pinion being driven from the pinion 16 attached to a shaft 18 meansof intermeshing wheels 19. 20. The gear ratio should be such as forinstance to allow the sha ft 78 to make a sen'iirevolution for a motionof the shaft 18, corresponding to the distance between two teeth of thepinion 16. When the drum 77 has turned 90 from the position shown in thefigure, the pecimen is demagnetized, but when it has turned 180 thespecimen is again magnetized. Compensation for eventual variations isalso made in this construction by inserting a standard specimen in thecoil :2 and by adjusting the air gaps until the correct indication ofthe galvanomcter is obtained. The air ga s are in this case adjusted byarranging tie steel magnet so that it may be moved longitudinally, sincethe ends of the ma net 53 pass through the non-magnetic shield 84 bywhich they are guided, whilst the curved part of the magnet 53 is guidedby a bolt 89 attached to the cross-piece 86 fixed to the frame of theapparatus. The. upper part of the bolt is threaded and fitted with a nut90 outside the magnet. Inside the magnet, between the magnet and thecross-piece 8G is a strong spring 91 which holds the magnet back. Thehorizontal position of the magnet will thus be controlled by. the nut90. By turning this nut inward the magnet is moved toward the ironpieces 79 and 80, so that the air gaps are diminished. By turning thenut outward the magnet is moved backward and the air gaps between themagnet 53 and the iron pieces 79 and 80 are increased. In order toprevent leakage of magnetic flux from the magnet 53 to the screens 5 and(5 while the iron pieces 79 and 80 are turned away, the shaft 78 may beprovided with an armature 81 of soft iron which then directly closes themagnetic circuit. Such an armature has moreover an important task inceit acts as an armature for the magnet when the apparatus is not in use.The resting position of the drum should therefore be 90 degrees from theposition shown in Figure 2.

However, independently of the method used for magnetizing anddemagnetizing the specimen, that is, for closing and breaking a magneticfield flowing through the screens 5 and 6 to the specimen, the coil 2 inwhich the loss is induced may be placed in any part of'the magneticcircuit. For instance, it may be placed on the screen (5, as shown inFigure 5. Between the free ends of the screens 5 and 6 a magnetic fluxmay, as above described, be introduced or cut OH. The change of thefield on mag netizing and demagnetizing the specimen takes place notonly in the specimen itself but also in the screens or the pieces 5 and6.

For compensation of eventual variations in the magnetic circuit it issuitable in addi tion to the adjustable air gap according to Figure 2.to use a removable magnetic shunt. Such a shunt is shown in Figure 4, inwhich figure the other parts of Figure 2 for sake of clearncss arepartly omitted. 1

As evident from Figure 4 the magnetic shunt is obta'ned by means of softiron piece (38 which projects from the upper pole of the magnet 53, anda soft iron piece 68 which projects from the lower pole of the magnet.Between the projecting ends of the pieces 68, 68 is asoft iron piece 71arranged in a shaft 72 which is pivotally mounted in the support 76which as well as the shaft 72 must be of non-magnetic material. Theshaft 72 is provided with a handwheel 73 by means of which the ironpiece 71 may be adjusted in every desired position in relation to theiron pieces 68, 68 for variation of the magnetic shunt.

i In such an apparatus the magnetic circuit first is approximatelyadjusted by regulating I the air gaps by means of the nut 90, Figme 2,and then the exact adjustment is obtained by means of the magnetic shunt68, 8 71. The arrangement for driving the shaft 18 and the pinion 16cooperating with the pinion 82 by means of the gear already mentioned,is also shown in Figure 2. The shaft 18 may be assumed to be driven by aclockwork.

lVhen the clockwork is started the pinion 16 rotates and causes theshaft 7 8 to rotate.

20 The magnetic circuit from the permanent magnet 53 through thespecimen is thus .closed and broken, and the specimen 1 inserted in thecoil 2, is thus magnetized and demagnetized.

As above pointed out, the indication of the magnetic loss in thespecimen should be read from the ballistic gralvanometer 4 only after asntlicient number of magnetizations and demagnetizations has been made.

Only in this way the loss is rendered practically constant, as mentionedabove, so that the percentage of carbon of the specimen can bedetermined by measuring the amount of the loss. The galvanometer mustnot be connected during these preliminary magnetizations, as it wouldnot then be still when the definite reading is to be made. Thegalvanoineter may be connected, for instance in the way shown in Figure2. The circuit from the coil 2 is closed over the outer contact 29 ofthe galvanomctcr 4. over the outer contact 30 to the lever 21 and, whenthe end 24 of this lever is moved upward. to the contact spring,- 22 andfrom this spring back cuit of the galvanometer is thus broken at thecontact pin 28. In order to keep the galvanometer still damped it isshunted by means of a suitable 'resistance'31 over the contact lever 21and the lower spring 23 by the aid of a contact 27. The lever 21 israised by the tooth 26 of the cam 25. This is'to be made." The'cam 25 isfor this-purpose fixed on the same shaft 18 as the pinion l6. Theclockwork and this shaft18 are released by pressing a button 44 whichacts upon'astopping lever 35 fitted with a catch 36. .The catch 36engages the teeth of the cam 32, also fixed on the shaft 18. As will beseen this cam 32 has only two teeth 33 and 34. In the original position(not that shown in the Figure 2) the tooth 34 rests against the catch 36of the lever 35. After to the coil 2. During the preliminarymagnetizations the end 24 is not raised, the 011'- i is effected onlywhen the definite indication the iron specimen has'been inserted in itsI pressed. against the support 39 attached to the arm 42. The fore endof the lever 38 thus moves upward and raises the end 37 of the lever 35but only for a moment suflicient to raise the catch 36 over the tooth34. \Vhen the end 37 has been raised somewhat the end of the lever 38slides off the end 37 when the lever 35 and the catch 36'again fall downon to the cam 32. As no tooth now. holds the catch 36, the clockworkrotates and the pinion 16 causes the shaft 78 to rotate for effectingthe preliminary magnctizations, as previously described. After a certainnumber of these magnetizations have been made the clockwork is stoppedby the catch 36 striking the tooth 33 of the cam 32. The cams then comeinto the positions shown in Figure 2. lVhile the cams are rotating, orafter they have been stopped, the button 44 should be released. Onreleasing this button, lever 42 swings on its pivot in the oppositedirection, thus carrying the lever 38 into contact with the end 37 oflever 35,"thereby. swinging. the lever 38 on its pivot intoya positionat an angle to the lever 35 whereby theend of the lever '38 is permittedto pass the end 37 and resume its position below the same, the spring40, which is placed under tension by the swinging of lever 38, actingtocause the lever to assume said position, as will be obvious from Fig.2. For reading the indication of the galvanoineter 4 the button 44 isnow pressed once more. The end 37 is then again raised so that 'thecatch 36 releases the tooth 33 but falls down immediately when the lever38 passes the end 37 as previously described. On the second pressing ofthe button 44 the clockwork. turns the shaft 18 only the part'of the waycorresponding to the distance between the teeth 33 and 34 of the wheel32. By this turning the tooth 26 opcrates the lever 21. The catch 24 of,the

lever 21 is hereby immediately raised by the tooth 26, so that the lever21 and the spring 22 come into contactby the aid of the con tact 28. Thereadin of the galvanometer 4 then takes place. he catch 24' now fallsdown from the tooth 26, breaking the circuit at the contact 28, butclosing it at the contact 27. Thisclosing must take place immediatelybefore the pointer of the galvanometer returns from the indication backto zero. The resistance 31 is in this case so regulated that the motionof the moving coil of the galvanometer is damped or stopped and compelsthe pointer to stop on zero or close to it. The moment for releasing thebutton 44 has obviously nothing to do with fixed. The spring' '40 holdsthe lever 38 this" damping. However, after the button has been releasedthe lever 38 returns to its original position below the end 37 as beforedescribed. By means of such a device which, of course, maybe made inmany various ways, any chance of omitting the preliminarymagnetizationsisv prevented, and at the same time it ensures thesame'number of magnetizations always being made.

Having now particularly described the nature of our invention and themanner of its operation, what we claim is:

1. Apparatus for determining the percentage of carbon in a specimen ofiron or steel,"

mg the specimen to be tested, and a perma nent magnet for magnetizingsaid specimen, an induction coil wound upon a portion of said circuit, apart of said magnetic circuit being movable with relation to the otherpart, means for repeatedly varying the magnetic force between two chosenvalues, an a measuring instrument for measuring the difference betweenthe magnetic fluxes through the specimen at said two values.

3. Apparatus for determining the percentage of carbon in a specimen ofiron or steel, which comprises a magnetic circuit. including thespecimen to be tested, and a permanent magnet for magnetizing saidspecimen, an induction coil upon a portion of said circuit, saidmagnetic circuit containing an adjustable air gap, means for repcatedyvarying the magnetic force between two chosen values, and a measuringinstrument for measuring the difference between the magnetic fluxesthrough the specimen at said two values.

4. Apparatus for determining'the percentage of carbon in a specimen ofiron or steel, comprising a magnetic circuit including the specimen tobe tested, and a permanent magnet for magnetizing said specimen, aninduction coil wound upon a portion of said circuit, and a removablemagnetic shunt, means for repeatedy varying the magnetic force betweentwo chosen values, and a measuring instrument for measuring thediflerence between the magnetic fluxes through the specimen at said twovalues.

5. Apparatus for determining the percentage of carbon in a specimen ofiron or steel, comprising a magnetic circuit including the specimen tobe tested and a. permanent magnet formagnetizing said specimen, aninduction coil woundupon a portion of said air- 'cuit, magnetic screensfor preventing speci- .mens of different lengths from exerting anyinfluence upon the result and insuring that the same length of specimenis included in the magnetic circuit when the determination is beingmade, mg the ma values, an

means for repeatedly varyetlc force between two chosen a measuring.instrument for measuring the difference between the magnetic fluxesthrough the specimen at said two values.

6. Apparatus for determining the percentage of carbon in a specimen ofiron or steel, comprising a magnetic circuit including the specimen tobe tested, and a permanent mag the specimen.

8. Apparatus for determining thepercent- I age of carbon in a specimenof iron or steel, comprising a magnetic circuit including the specimento be tested, and a permanent magnet for magnetizing said specimen, aninduction coil wound upon a portion of said circuit, a measuringinstrument adapted to be placed in circuit with said induction coil,.

and means for maintaining the induction coil and measuring instrumentout .of electrical connection during a predetermined time andautomatically operative to connect said measuring instrument andinduction coil after said predetermined time.

In testimony whereof we have signed our names to this specification.

CARL JOHAN GUNNAR MALMBERG. JOHAN QUNNAR HOLMSTRflli/l.

JIM)

